Pests

Squash bug
Squash bug. Photo credit: 1

By Eric Sideman, Ph.D.

Fall chores are my favorites. At no other time do I have more hope for a successful garden than the fall before. Autumn is even better than spring, especially last spring when we all realized very early in April that it was not going to be the best year. Many hopes were dashed last spring before the ground was dry enough to till. Fall chores, on the other hand, not only hold high hope for future harvests, but those enjoyable fall chores can add greatly to the likelihood of avoiding a few pests and diseases next year.

Crop Rotation Foils Some Pests

The first fall chore is to begin planning where you will plant crops next year based on problems you had this year. If you have more than one garden, your strongest tool is crop rotation. The goal is to keep crops that host the same problems moving between or among gardens so that pests waking up in the spring cannot find a host. If you have only one garden, rotation is still very useful for soil husbandry and weed control, but does not serve well for pest management.

Three criteria about pests determine whether rotation will help. First, how well can the pest (disease or insect) move from one place to another? If you have only one garden, crop rotation will not help prevent pest problems, because almost anything can move from one side of a garden to the other to find a host. But many insects and diseases have very limited dispersal, and sometimes just 500 feet between fields or gardens can be a barrier.

Second, how long can the problem persist in the soil without a host? Some spores can survive in a resting stage for a decade without a host, so you will not eliminate them by rotating crops. But most insects and many diseases need a new host plant when they arise in the spring.

Third, how specific to a particular crop is the pest? If a pest can survive year to year feeding on plants other than your particular crop, then it can pass the years waiting for your crop to return. The tarnished plant bug, for example, feeds on several crops and on about 300 species of weeds, so rotation will not control it.

 Anthracnose of tomato
Anthracnose of tomato.
Photo credit: 2

Sanitation Cancels Winter Vacation

Sanitation is another powerful tool. Knowing where the pest spends the winter, you can try to make winter survival less successful. Many pests hide under crop and other plant debris. Others dig into the soil. Some survive only on living tissue or debris of the host. If you put crop debris that is infested with such a disease into a compost pile, then you have to ensure that the compost pile gets hot enough to kill the spores (131 degrees F. usually does it) and that every bit of it gets hot, or do not use that compost on susceptible crops the next year. Think about that in the fall when you are cleaning up.

Fall chores can help control the following pests:

Onion maggot – Damaged bulbs are the major food source for late-season onion maggots, and these maggots become the overwintering pupae. Remove all cull onions from the field after harvest. Culls should not be disked in until after the last summer generation of flies has had its flight period, because disking promotes larval survival by increasing the number of sites available for larvae to enter the onion.

Onion neck rots, leaf blights and purple blotch – These diseases overwinter primarily in onion plant debris and cull piles. Get rid of as much onion debris as you can, destroy cull piles and, if you can, rotate with nonhost crops such as carrot, celery, lettuce or potato.

Squash bug – The squash bug overwinters as an adult in sheltered places, under tall grass and plant debris, along fence rows and in buildings. Removing potential overwintering sites and rotation can help reduce the number of adults that survive the winter to lay eggs next June.

Septoria leaf spot on tomato
Septoria leaf spot on tomato. Photo credit: 3

Blights and leaf spots of cucurbits – Many of these are caused by fungi that overwinter on infested crop debris, and some overwinter in seed. Make sure you use pathogen-free seed. Destroy crop debris promptly after harvest. Crop rotation is the best means of control.

Anthracnose of tomato – This fungus survives from season to season on infected plant refuse and in the soil. Rotation at least every two years is the best approach to protect tomatoes. Removing and destroying infected fruit at the end of the season prevents inoculum from building up in the soil. Some weeds carry the disease, so destroying weeds in the fall helps, too.

Septoria leaf spot on tomato – Septoria overwinters on infected tomato debris or debris of Solanaceous weeds, such as horsenettle or nightshade, and on stakes and cages. Infected seed can be a problem, too, so know your seed source. Do not save seed from diseased plants. A one- to two-year rotation between tomato crops is important, as is weed control, and removing crops and weed debris in the fall helps.

Late blight of potato and tomato – This disease is rare in Southern Maine, but it is a very big problem in some seasons. In The County it is a regular problem. Everyone should practice good sanitation, because neighbors’ actions really count. The fungus overwinters only on living tissue. In Maine, that means primarily on potato tubers in cull piles or on volunteers, which are sources of the initial infection. During the season wind-blown spores from diseased potato or tomato plants can travel long distances, so the key to prevention is to minimize the initial infection in the spring by managing the culls. Eliminate all cull piles and minimize tubers left in the field. Kill volunteer sprouts early in the spring.

European corn borer
European corn borer. Photo credit: 4

European corn borer – Corn may be this insect’s favorite host, but it also feeds on about 200 other species, including peppers, snap beans and potatoes. The larvae of this pest overwinter in the bottom part of corn stalks. Fall plowing and spring disking can eliminate 75% of overwintered larvae in a corn field. Shredding plant residue also destroys borers in stalks and stubble. Some growers may think about the old practice of burning stalks in the field after harvest, but this has negative environmental impact.

Fall cleanup and planning can help eliminate or minimize many other plant pests next year. Think about problems that you had this year and learn the life cycle of the pest. If you need help finding information, contact me.

About the author: Eric is MOFGA’s director of technical services and can answer your farming and gardening questions at [email protected] or 946-4402.

Photo credits

1. Squash bug. University of Maine Pest Management Lab Fact Sheet, “Sucking Insects that Affect Vegetable Plants,” https://pmo.umext.maine.edu/factsht/suck.htm.

2 Anthracnose of tomato. From “Fresh Market Tomatoes,” by Henry G. Taber, Mark L. Gleason, and Donald R. Lewis, Iowa State University, 1998; at www.public.iastate.edu/~taber/Extension/tomatoes/tomatoes.html.

3 Septoria leaf spot on tomato. From “Fungal Leaf/Fruit Spots of Tomato,” University of Conn. Integrated Pest Management; at www.hort.uconn.edu/ipm/veg/htms/todispic.htm.

4 European corn borer. From “European Corn Borer,” by James F. Dill and David T. Handley, University of Maine Cooperative Extension Pest Management Office, at https://pmo.umext.maine.edu/swetcorn/european.htm.

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